It is the first US airport after crossing the Atlantic...
It has a HUGE ramp and is easy to isolate an aircraft if needed....
There is a US Federal Court House in town, so it's easy to prosecute....
There are US Customs, US Imigration and FBI Offices in town....

"It's not the size of the dog in the fight, but the size of the fight in the dog"

The real question is why were these pax not stopped before they boarded. AFAIK the FIS has access to PNR records pre-departure, so unless these guys were NOREC's or LMC transfer pax, they should have been spotted and flagged way before the plane left France. No doubt US authorities went for the more dramatic course of action designed to garner maximum publicity for their anti-terrorism activities, which in this instance resulted in errrm no arrests and errrm no convictions. Good job !